Japanese Patent Laid-Open No. 2007-305675 discloses a technique for reducing an influence that infrared light exerts on an optical black portion (to be referred to as an OB portion hereinafter). Also, Japanese Patent Laid-Open No. 2008-016733 discloses a technique for preventing the adverse effect of light which enters an effective pixel portion from the front surface side of a semiconductor substrate in a back surface incidence type solid-state image sensing apparatus.
Although infrared light can be shielded by a light-shielding film, it is harder to absorb than visible light and therefore has a penetration distance longer than that of visible light. For this reason, infrared light which obliquely enters the effective pixel portion on the light-receiving surface is transmitted through the semiconductor substrate, is reflected by the surface opposite to the light-receiving surface, and enters a sensor portion in the OB portion. In this case, photo-electric conversion occurs in the OB portion, so a black level to be detected in the OB portion under normal circumstances may not be correctly detected.
Also, to improve the aperture ratio, another back surface incidence type solid-state image sensing apparatus has been proposed. In this apparatus, a sensor portion which performs photo-electric conversion and plural layers of wiring lines including a signal line for driving the sensor portion are formed on the front surface side of a semiconductor substrate. This apparatus has a light-receiving surface on the back surface side of the semiconductor substrate. However, this structure poses a problem that infrared light enters the OB portion in relatively large amounts although it can improve the aperture ratio.
FIG. 4 is a sectional view showing the schematic arrangement of a conventional back surface incidence type solid-state image sensing element. A light-shielding film 30 for shielding an OB portion is formed above a sensor portion 11 and opens to an effective pixel portion 41 of a pixel within the effective pixel portion 41, as shown in FIG. 4. Infrared light strikes the light-receiving surface of a semiconductor substrate 10. Then, it is often the case that infrared light L which obliquely strikes the semiconductor substrate 10 is transmitted through the semiconductor substrate 10, is reflected by the inner surface of an insulating layer 20 on the side opposite to the light-receiving surface, and enters the sensor portion 11 of a pixel within an OB portion 42, as shown in FIG. 4.
Infrared light is harder to absorb than visible light, but is absorbed albeit poorly. Especially infrared light with a wavelength of about 800 nm to 1,300 nm is absorbed by silicon to some extent. For this reason, when infrared light enters the sensor portion 11 of a pixel within the OB portion 42, it is absorbed by the sensor portion 11 and photo-electric conversion occurs in the OB portion 42.
As a measure against the above-mentioned phenomenon, it is possible to form an image sensing apparatus such as a camera by placing an IR cut filter in front of a solid-state image sensing element. Using an IR cut filter in this way makes it possible to prevent infrared light from entering not only the OB portion but also the effective pixel portion. However, an IR cut filter capable of cutting light in a wide wavelength range is very expensive, so its use raises the cost of the image sensing apparatus. Furthermore, the measure of using an IR ct filter cannot be adopted in, for example, an image sensing apparatus which cannot employ an IR cut filter (for example, a monitoring camera which utilizes infrared light or an image sensing apparatus which enhances the resolution by utilizing infrared light).